Many commercial products are temperature sensitive and can spoil, deteriorate or lose quality if they suffer even brief exposure to a temperature near or below freezing. For example, fruits may turn brown, flowers, salad greens and some herbs may wilt and vaccines may lose potency. Other foodstuffs and medications as well as some industrial products, for example latex paints, are also freeze sensitive.
Accordingly there is a need for a low-cost freeze indicator which can be associated with a freeze-sensitive host product, for example by attaching the freeze indicator to the host product, and which can provide an irreversible indication of past exposure of the host product to freezing or near freezing temperatures.
A number of proposals for such freeze indicators is known. For example, U.S. Pat. Nos. 7,343,872 and 7,490,575 and U.S. Patent Application Publications Nos. 2008/0110391 and 2008/0257251, all having inventors Taylor et al. and being assigned to Temptime Corporation disclose a variety of freeze indicators and freeze indicator technologies. These patents and the patent application publications are referenced herein as the “Taylor et al. patent publications”, and each one is incorporated by reference herein.
As described in their specifications the Taylor et al. patent publications disclose freeze indicators which employ an indicator element comprising a dispersion of solid particles in a liquid medium. The indicator element can change appearance irreversibly upon exposure to freezing temperatures, for example as a result of coagulation of the dispersed solid particles, providing a signal that the freeze indicator has been exposed to a freezing temperature.
In addition, U.S. Pat. No. 4,191,125 to Johnson and U.S. Pat. No. 5,239,942 to Ignacio et al. disclose freeze indicators comprising frangible ampoules. U.S. Pat. No. 4,148,748 to Hanlon et al. (“Hanlon”) discloses a nonreversible freeze-thaw indicator employing a colloidal dispersion of material in latex form. As described in Hanlon, the latex can comprise styrene or other polymers. U.S. Pat. No. 4,846,095 to Emslander et al. and U.S. Pat. No. 5,964,181 to Pereyra disclose freezing point or critical temperature indicators wherein the appearance of a microporous sheet is changed by wetting the microporous sheet with a freeze-sensitive composition. U.S. Pat. No. 6,837,620 to Shahinpoor describes a shape memory alloy temperature sensor that changes shape when exposed to temperatures below a start temperature. U.S. Pat. No. 6,472,214 to Patel describes a freeze monitoring device which comprises an activator solvent which is miscible with water above a threshold temperature and which separates out below a threshold temperature.
Furthermore, U.S. Pat. No. 6,957,623 Guisinger describes a critical temperature indicator which produces a visual, irreversible indication that the indicator has been exposed to a critical temperature such as a temperature near the freezing point of water. As described, Guisinger's critical temperature indicator includes a transformable material including a mixture of water, a nucleating agent, latex, and a stabilizer for the nucleating agent. As described, in the patent, the latex can be a wax. Also, the nucleating agent can be an ice nucleating active (INA) microorganism and the water can comprise deuterium oxide.
U.S. Pat. No. 5,223,412 to Wight et al., U.S. Pat. No. 5,137,815 to Hendricks and U.S. Pat. No. 5,489,521 to So et al., describe ice nucleating agents and microorganisms that can be employed as ice nucleating agents.
Notwithstanding the foregoing proposals for freeze indicators it would be desirable to have a freeze indicator having new response characteristics.
The foregoing description of background art may include insights, discoveries, understandings or disclosures, or associations together of disclosures, that were not known to the relevant art prior to the present invention but which were provided by the invention. Some such contributions of the invention may have been specifically pointed out herein, whereas other such contributions of the invention will be apparent from their context. Merely because a document may have been cited here, no admission is made that the field of the document, which may be quite different from that of the invention, is analogous to the field or fields of the present invention.